Tears keep the delicate surface of an eyeball clean and wet. Tears are produced in glands above an outer corner of the eye, and they spread across the eye surface with each blink and form a layer of moisture, or tear film, that serves as a protective coat for lubricating the eye and washing away foreign bodies that might cause harm or obscure vision. Tears that wash across the eye naturally evaporate into air or drain into tear ducts. Normally, the eye constantly bathes itself in tears by producing tears at a slow and steady rate so that the eye remains moist and comfortable. However, many people that wear contact lenses or have dry eyes in general may need to apply tear drops to keep their eyes properly hydrated. Yet those individuals may go about the day without knowing that their eyes are too dry or not optimally hydrated with tear fluid.